18 December 2004 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a trough in the Stygis Catena region east of the martian volcano, Elysium Mons. The trough probably formed by collapse. Large, dark boulders can be seen on the trough floor in this volcanic region. The image is located near 24.4N, 210.4W. The image covers an area about 3 km (1.9 mi) wide and sunlight illuminates the scene from the lower left.